1. Field of the Invention.
The present invention relates to the field of wireless local area networks (LANs) and, more particularly, to a method and apparatus for implementing self-organization in a wireless LAN.
2. Description of the Related Art
Through the merging of computer and communications technology, computer networks have greatly enhanced the computing power available to the individual computer user linked to other computers in a network. Not only do networks provide for the exchange of information between autonomous computers, but they also enable each user or "node" to share resources common to the entire network. Through resource sharing, all application programs, databases and physical equipment in the network may be made available to any node without regard to the physical location of the resource or the user.
As for the linkage between nodes, there are generally two types of network interconnections. The nodes in a wired network communicate with each other by using transmission lines to carry the signals between the nodes. The nodes in a wireless network, on the other hand, communicate with each other using radio signals or other types of wireless links rather than physical interconnections.
One type of wireless network is a wireless local area network (LAN). A LAN is local in the sense that the transceiver nodes are located within a radius of only a few miles of each other. As such, the proximity of the nodes permits the network to operate reliably at low power and at high data rates.
Typically, nodes in a wireless LAN are mobile and transmit information in packets. These nodes, although mobile, may be geographically grouped at any given time into basic service areas (BSAs), otherwise referred to as "cells." The nodes within a cell communicate with each other either directly or through a cell coordinator that relays messages among the nodes of the cell. Note that the coordinator itself may be implemented either within a regular node or in a node that only performs the coordination function.
Communication between nodes in different BSAs is accomplished through an access point (AP), which is responsible for relaying packets into and out of the BSA. To allow for inter-cell communication, each cell must contain at least one AP. The coordinator and the AP are often implemented in the same node. Communication among the APs may take place over the same or different radio channels or via a separate wired network.
During node power-up, the node is assimilated into the network environment using what is known as the network "basic self-organization" ("BSO") capability. During self-organization, each node is associated with a coordinator in a cell (if one exists), and in a multi-cell system, each node is also associated with at least one AP in a cell. For ease of explanation, APs and coordinators will be collectively referred to as "relay points". The choice of which relay point to associate with a node is based on criteria such as the quality of the link between the node and the relay point, and the load carried by the relay point. The self-organization procedure is considered complete when a node has acquired the context parameters that will enable it to effectively communicate within the cell with peer nodes or relay points. For example, the node will need to know the operating frequency of the coordinator before it can begin to communicate with the coordinator.
The need for a self-organization capability depends on the medium access protocol and the BSA architecture used by the network. In a completely uniform and distributed system, a self-organization capability is unnecessary because all nodes operate identically using the same operating parameters. Thus, a node need not acquire context parameters to establish communications with a relay point because the parameter information is fixed in the node since it is the same for all nodes and relay points. For instance, if all nodes and relay points operate at the same frequency, then there is no need for a node to acquire this information during power-up because the node frequency need never be adjusted and the frequency value may be permanently stored in the node. As a practical example, the single-band ALOHA system is uniform and completely distributed, and thus does not require a self-organization capability. On the other hand, when the network is not completely distributed, or if the BSAs utilize different operating parameters, as may be the case if the cells are designed to achieve non-interference, then a separate self-organization process is necessary.
In conventional cellular telephone systems, the association of a mobile unit with a base station is determined by the base stations alone. Because the mobile units do not participate in the BSO process, the cellular phone system requires a considerable amount of cooperation among the base stations to ensure an adequate association. The quality of the association and the efficiency of the process in the cellular telephone system is not as good as that which would be achieved if the mobile unit participated in the self-organization procedure. For example, in a conventional cellular telephone system the base stations communicate with each other to determine which station best receives signals transmitted by the node. However, the radio links are asymmetric, and the signal characteristics transmitted are not necessarily the same as those received. Thus, a base station cannot determine how well a node receives a signal transmitted by the station based upon how well the base station receives a signal from the node. Clearly, optimal association requires the participation of the node in the BSO process.